Polarizing plate

ABSTRACT

A polarizing plate with which a drop in polarization efficiency, hue shift, and light leakage do not substantially arise, under a high humidity/high temperature environment is provided. The polarizing plate of the present invention comprises a polyvinyl-alcohol-based polarizing film, a protective film having thereon two anchor coat agent layers, mainly composed of a cyclic-olefin-based resin, laminated on at least one side of the polarizing film, with an adhesive. The amount of change in optical in-plane retardation of the protective film is 5 nm or less after 24 hours in an atmosphere of 80° C., and the wetting tension of the anchor coated surface of the protective film is 500 μN/cm (23° C.) or more. The anchor coat agent layers include a first layer made of polyisocyanate and polyester polyol and/or polyether polyol, and a second layer made of polyvinyl alcohol. The adhesive is made of polyvinyl alcohol.

TECHNICAL FIELD

[0001] The present invention relates to a polarizing plate, particularlyto having high durability and high polarization efficiency that isuseful for liquid crystal displays (LCDs) and more specifically, to animprovement in a polarizing plate for substantially preventing mainlydrop in polarization efficiency, hue shift, and light leakage even undera high humidity/high temperature environment.

BACKGROUND ART

[0002] A conventional polarizing plate with high polarization efficiencyis generally such that a cellulose-triacetate-based (hereinafter,referred to as TAC) film, which serves as a protective film, islaminated on a polarizing film in which iodine or a dichroic dye isadsorbed and oriented in a polyvinyl-alcohol-based (hereinafter,referred to as PVA) film with an aqueous solution of PVA resin, whichserves as an adhesive, in a state of wet or semidry flowability.

[0003] However, since the water absorption and water vapor permeabilityof TAC is high in a polarizing plate using TAC for the protective film,deterioration in polarization performance under a high humidity/hightemperature environment, specifically, drop in polarization efficiency,hue shift, and light leakage under crossed nicols, has been significant.

[0004] In order to overcome these problems, polarizing plates that use afilm made of a resin with low water absorption and low water vaporpermeability for the protective film have been proposed.

[0005] For example, Japanese Unexamined Patent Publication No. 7-77608discloses a polarizing plate such that a film serving as a protectivefilm and made of a thermoplastic saturated norbornene-based resin isadhered to a PVA-based polarizing film using an acrylic-based adhesiveor a polyester-isocyanate-based adhesive. After such a polarizing plateis subjected to an environment of 80° C. and 90%RH for 500 hours, thepolarization efficiency is 95% or higher and the single transmissivityis 38% or higher.

[0006] In addition, Japanese Unexamined Patent Publication 7-294732discloses a polarizing plate such that a film having a photoelasticcoefficient of 25.0×10⁻¹³ cm²/dyne or less, for example, a film made ofan amorphous polyolefin as Zeonex, or polymethyl methacrylate such,serves as a support for a polarizing element film, and the support isadhered to the polarizing element film using an acrylic-based adhesive.After such a polarizing plate is subjected to an environment of 60° C.and 90%RH for 100 hours, the pyschometric lightness is small.

[0007] However, although these polarizing plates are able to suppress adrop in polarization efficiency under a wet heat environment, it cannotbe said that suppression of hue shift and light leakage is sufficientlyrealized.

DISCLOSURE OF THE INVENTION

[0008] In the view of the foregoing and other problems, it is an objectof the present invention to provide a polarizing plate with which, notonly suppression of a drop in polarization efficiency is achieved, butalso with which hue shift and light leakage do not substantially arise,under a high temperature/high humidity environment.

[0009] A polarizing plate of the present invention comprises apolyvinyl-alcohol-based polarizing film, a protective film, mainlycomposed of a cyclic-olefin-based resin having thereon two anchor coatagent layers, laminated on at least one side of the polarizing film withan adhesive.

[0010] The amount of change in optical in-plane retardation of theprotective film is 5 nm or less after 24 hours in an atmosphere of 80°C., and the wetting tension of the laminated surface of the protectivefilm is 500 μN/cm (23° C.) or more.

[0011] A first anchor coat agent layer is made of polyisocyanate andpolyester polyol and/or polyether polyol. A second anchor coat agentlayer is made of polyvinyl alcohol.

[0012] The adhesive is made of polyvinyl alcohol.

[0013] The polarizing film of the present invention is produced byuniaxially stretching and orienting a film made of PVA or a derivativethereof, and subsequently, adsorbing iodine, carrying out a boric acidsolution treatment, and drying the film while under tension. Such a filmalso may be produced by immersing a film made of PVA or a derivativethereof in an aqueous solution of iodine such that the iodine isadsorbed, and subsequently, uniaxially stretching and orienting the filmin a boric acid solution and drying the film while under tension.Polarizing films that utilize dichroic dyes, such as those that areazo-based, anthraquinone-based, and tetrazine-based, instead of iodineare fabricated in the same manner as well.

[0014] The polarization efficiency of a polarizing film obtained in sucha manner is preferably, 95.0% or higher, more preferably, 99.0% orhigher, and even more preferably, 99.7% or higher.

[0015] Hue shift as referred to in the present invention denotes aphenomenon such that when a single polarizing plate or crossed nicols isplaced in a wet heat atmosphere, hue shift occurs with the singlepolarizing plate or the crossed nicols.

[0016] When a liquid crystal display employing polarizing plates withwhich hue shift arises is used for a long period, the hue of the displaychanges and contrast deteriorates, becoming one cause of deteriorationin the performance of the liquid crystal display.

[0017] Light leakage as referred to in the present invention denotes aphenomenon such that in-plane luminance changes when two polarizingplates arranged to have a crossed nicols relation are placed in a wetheat environment.

[0018] When a liquid crystal display that employs polarizing plates thatgenerate light leakage is used for a long period, light leaks at theedges of the display when black is displayed, and thereby displaycontrast deteriorates, becoming one cause of deterioration in theperformance of a liquid crystal display.

[0019] Having fully considered how to provide a polarizing plate withwhich, not only suppression of a drop in polarization efficiency isachieved, but also with which hue shift and light leakage do notsubstantially arise, under a high temperature/high humidity environment,the present inventors came to the following conclusion, by which thepresent invention was achieved.

[0020] First, suppression of a drop in polarization efficiency under ahigh temperature/high humidity environment can be achieved by using afilm with low water absorption and low water vapor permeability for theprotective film of a polarizing plate. Suppression of hue shift under ahigh temperature/high humidity environment can be realized bysufficiently adhering a polarizing film and a protective film and bysuppressing reversion in the alignment of the polarizing film.Suppression of light leakage under a high temperature/high humidityenvironment can be realized by using a film having a small amount ofchange in optical in-plane retardation for the protective film of apolarizing plate.

[0021] The present inventors then fully considered how to substantiatethese inferences.

[0022] For the present invention, a film mainly composed ofcyclic-olefin-based resin was employed for the protective film of thepolarizing plate, because such a film has low water absorption and lowwater vapor permeability, and various physical properties required of aprotective film for a polarizing plate, such as light transmissivity.(In addition, because cyclic-olefin-based resin has a small photoelasticcoefficient, it was conjectured to be useful in preventing lightleakage.)

[0023] In the present invention, cyclic-olefin-based resin is used as ageneral term, specific examples (a) to (d) being shown below.

[0024] (a) polymers that are ring-opening (co-)polymers of cyclic olefinwith hydrogen added as needed

[0025] (b) (co-)polymers with cyclic olefin attached

[0026] (c) random copolymers of cyclic olefin and an a-olefin such asethylene or propylene

[0027] (d) graft modified substances that result when the above (a) to(c) are modified with unsaturated carboxylic acid or derivatives thereof

[0028] The cyclic olefin is not particularly limited, examples includingnorbornene, tetracyclododecene, and derivatives thereof (for example,substances containing a carboxyl group or an ester group).

[0029] Known additives such as ultraviolet absorbers, organic orinorganic antiblocking agents, slip additives, antistatic agents, andstabilizers may be added appropriately to the cyclic-olefin-based resin.

[0030] The method of forming a protective film from cyclic-olefin-basedresin is not particularly limited, it being possible to employ methodssuch as solution casting, extrusion, and calendering.

[0031] Examples for a solvent used in solution casting include alicyclichydrocarbons such as cyclohexane and cyclohexene and derivativesthereof, as well as aromatic hydrocarbons such as toluene, xylene, andethyl benzene and derivatives thereof.

[0032] The thickness of the protective film is commonly 5-150 μm,preferably 10-100 μm, and more preferably 20-60 μm. When thickness istoo thin, a film tends to be difficult to handle and when thickness istoo thick, the amount of change in optical in-plane retardation tends tobe large.

[0033] In order to determine the relationship between hue shift and theadhesive strength of a protective film/polarizing film under a hightemperature/high humidity environment, tests were carried out usingvarious adhesives with varying adhesive strength, and as was initiallypredicted, it was determined that there is a correlation between hueshift and the adhesive strength of a protective film/polarizing film.However, there was no adhesive with which hue shift substantially didnot occur. In consideration of this, the present inventors consideredvarious ways of increasing the adhesive strength and suppressing hueshift to the greatest possible degree and eventually, discovered twoways of overcoming the problems of adhesive strength and hue shift.

[0034] Specifically, first, the wetting tension of the surface of theprotective film to be anchor coated is made to be 500 μN/cm (23° C.) orhigher and preferably 550 μN/cm (23° C.). In order to achieve thisvalue, it is not necessary to employ a particular technique, it beingpossible to use a technique known in the art. Examples for a surfacetreatment include a corona discharge treatment, an ultravioletirradiation treatment, and a chemical treatment. The corona dischargetreatment or ultraviolet irradiation treatment may be carried out in airor in an atmosphere of nitrogen or a rare gas.

[0035] When the wetting tension is lower than 500 μN/cm (23° C.),sufficient adhesive strength cannot be obtained.

[0036] Secondly, an anchor coat agent made of polyisocyanate andpolyester polyol and/or polyether polyol is coated, as a first layer, onthe protective film surface and dried, then on the resulting film, ananchor coat agent made of polyvinyl alcohol is coated, as a second layerand dried, and subsequently, an adhesive solution of polyvinyl alcoholis adhered to the polarizing film in a wet or semidry state.

[0037] The coating and drying of the anchor coat agents for two layersmay be carried out directly before adhering the protective film and thepolarizing film with an adhesive solution, or the film may be woundtemporarily after coating the protective film surface with the anchorcoat agents for two layers and drying, and adhering of protective filmand polarizing film with an adhesive solution carried out at a latertime.

[0038] The polyisocyanate of the anchor coat agent for the first anchorcoat agent layer has two or more isocyanate groups in each molecule, thepolyester polyol of the anchor coat agent for the first layer has esterbonds in its molecules and two or more hydroxyl groups in each molecule,and the polyether polyol of the anchor coat agent for the first layerhas ether bonds in its molecules and two or more hydroxyl groups in eachmolecule.

[0039] The skelton structure of the polyisocyanate may be an aromaticring or another structure, a long chain alkylene group being preferablefrom the perspective of adhesive strength. This is thought to be becauselong-chain alkylene has a degree of flexibility and thus good adhesionwith the protective film surface is expected.

[0040] The mixing ratio of polyisocyanate and polyester polyol and/orpolyether polyol is preferably, 20:1-1:20 and more preferably, 5:1-1:5,in consideration of the equivalence weight ratio of the hydroxyl groupsand the isocyanate groups.

[0041] It is preferable that the amount of anchor coat agent be suchthat a thickness after drying of 0.001-5 μm results and more preferablethat a thickness of 0.01-2 μm results. When too little anchor coat agentis used, adhesive strength often cannot be realized to the degreedesired, and when too much is used, coating nonuniformities easilyarise, which is often undesirable in terms of hue shift and lightleakage.

[0042] Note that it cannot be said that substances that react withpolyisocyanate other than polyester polyol and/or polyether polyolmentioned above, for example, acrylic-based substances, sufficientlydemonstrate advantageous effects in terms of suppressing hue shift dueto there weak adhesive strength to the protective film.

[0043] The polyvinyl alcohol of the anchor coat agent for the secondlayer is mainly composed of a resin that is obtained by carrying out asaponification treatment on vinyl acetate resin. It is preferable thatthe degree of polymerization be 1000-3000 and that the degree ofsaponification be 85% or higher and more preferable that the degree ofpolymerization be 1500-3000 and the degree of saponification be 98% orhigher. Other monomers such as monomers copolymerized appropriately witha small amount of acrylic acid, crutonic acid, itaconic acid, and thelike or monomers modified by alkyl groups, epoxy groups, or the like maybe used.

[0044] A substance that reacts with polyvinyl alcohol, such aspolyisocyanate, boric acid, alkylene diamine, and epoxy resin, may beadded to the polyvinyl alcohol. Advantageous effects are obtainedparticularly with polyisocyanate in terms of improving in waterresistance and easy handling.

[0045] The advantageous effects of the second anchor coat layer are asfollows. First, the adhesive strength does not deteriorate for anextended period of time. When there is only the first anchor coat agentlayer present, because the layer contains isocyanates, the layer easilydeteriorates, and thus when only the first anchor coat is provided onthe protective film, and stored for an extended period of time and thenadhered to the polarizing plate, the adhesive strength is significantlyreduced. However, when the second anchor coat layer is provided, anadvantageous effect that the adhesive strength is not reduced for anextended period of time is obtained. Accordingly, a protective filmhaving thereon the first anchor coat layer and the second anchor coatlayer can be stored for an extended period of time, allowing theproduction and storing of the protective films in advance. Secondly, thesecond anchor coat layer has a degree of water absorbing property, andtherefore an advantageous effect is obtained that the layer speedilyabsorbs moisture in an adhesive solution when adhered to the polarizingplate to complete adhesion in a short time.

[0046] It is preferable that the amount of anchor coat agent be suchthat a thickness after drying of 0.01-30 μm results, more preferablethat a thickness of 0.1-15 μm results, and even more preferable that athickness of 0.5-5 μm results. When too little anchor coat agent isused, adhesive strength to the first anchor coat layer often cannot berealized to the degree desired, and when too much is used, the costeffectiveness decreases.

[0047] The polyvinyl alcohol of the adhesive is mainly composed of aresin that is obtained by carrying out a saponification treatment onvinyl acetate resin. It is preferable that the degree of polymerizationbe 1000-3000 and that the degree of saponification be 94% or higher, andmore preferable that the degree of polymerization be 1500-3000 and thedegree of saponification be 98% or higher. Other monomers such asmonomers copolymerized appropriately with a small amount of acrylicacid, crutonic acid, itaconic acid, and the like or monomers modified byalkyl groups, epoxy groups, or the like may be used.

[0048] It is preferable that the amount of adhesive solution be suchthat a thickness after drying of 0.01-10 μm results, more preferablethat a thickness of 0.02-5 μm results, and even more preferable that athickness of 0.05-3 μm results. When too little adhesive is used,adhesive strength often cannot be realized to the degree desired, andwhen too much is used, the cost effectiveness decreases.

[0049] A substance that induces reactive curing with polyvinyl alcohol,such as polyisocyanate, boric acid, alkylene diamine, and epoxy resin,may be added.

[0050] In order to determine the relationship between light leakage andthe amount of change in optical in-plane retardation under a hightemperature/high humidity environment, 50 μm thick protective filmshaving varying amounts of change in optical in-plane retardation andmainly composed of various cyclic-olefin-based resins, and polarizingplates were fabricated using these protective films. Investigation intothe amount of light leakage using a method described later revealed thatthere is a correlation between light leakage and the amount of change inoptical in-plane retardation, as was initially predicted, and it wasdiscovered that light leakage substantially does not occur when theamount of change in optical in-plane retardation is 5 nm or less.

[0051] In the tests, substances described previously were used for thelaminated surface of protective film, the anchor coat agents, and theadhesive.

[0052] The amount of change in optical in-plane retardation was obtainedas follows. As shown in FIG. 2(a), a protective film 3 cut to a sizelength×width=100 mm×100 mm was attached to a glass substrate 1 with abinder 2 made of acrylester-based base resin and an isocyanate-basedcuring agent interposed. The optical in-plane retardation was measuredin each of nine sections divided as shown in FIG. 2(b), and the averagevalue R₀ was obtained. After then subjecting this to an 80° C.atmosphere for 24 hours, the optical in-plane retardation was measuredin the same nine sections, and the average value R was obtained. Thedifference between R and R₀ (R−R₀) was taken to be the amount of changein optical in-plane retardation.

[0053] For the most part, the amount of change in optical in-planeretardation is dependent on distortion of molecular chains in theprotective film and on residual shrinkage percentage.

[0054] When a protective film is fabricated by solution casting,distortions in the molecular chains arise in the drying step. Inaddition, residual shrinkage percentage is affected by the orientationof the cyclic-olefin-based resin when the solution is stretched on ametal drum or an endless belt, by the orientation of cyclic-olefin-basedresin caused by pulling tension in the drying step, and by the residualsolvent.

[0055] When a protective film is fabricated by extrusion, distortions inthe molecular chains arise during cooling and hardening with a chillroll after extrusion from an extruder. In addition, residual shrinkagepercentage is affected by the draw during extrusion from the extruderand by the orientation of the cyclic-olefin-based resin caused bypulling tension from the point of cooling and hardening to the point ofwinding.

[0056] In order to make the amount of change in optical in-planeretardation of the protective film 5 nm or less, it is necessary toemploy suitable methods such as correcting distortions in molecularchains in the protective film and reducing the residual shrinkagepercentage.

[0057] For example, methods of correcting distortions of molecularchains and of reducing the residual shrinkage percentage include heatingthe film under a minus draw before winding the film and leaving theloosely wound film in a heat chamber. In addition, in the case ofemploying solution casting for production, leaving the film in a dryingoven for a long period is one method of reducing the residual solvent,preferably until none remains. Adding preferably 0.1-20% by weight, morepreferably 0.5-10% by weight, and even more preferably 0.5-5% by weightwith respect to resin of a plasticizer such as dioctyl adipate, dioctylphthalate, or isodecyl adipate to the casting solution before hand, isanother method. Because the drying time required for practicallyeliminating the residual solvent is reduced by ⅕-{fraction (1/20)} whena plasticizer is added, such a method is advantageous from theperspective of productivity and cost of equipment. The advantageouseffects of adding a plasticizer are conjectured to be as follows. Thatis, it is thought that because cyclic-olefin-based resin molecules havea bulky skelton structure, solvent that enters into these gaps does noteasily evaporate, but when a plasticizer is added, the plasticizerenters into the gaps so as to discharge the solvent from the gaps.

[0058] The residual shrinkage percentage necessary in order to make theamount of change in optical in-plane retardation of the protective film5 nm or less is such that surface shrinkage percentage according to ameasuring method described later is preferably 0.8% or less, morepreferably 0.5% or less, and even more preferably, 0.3% or less.

BRIEF DESCRIPTION OF THE DRAWINGS

[0059]FIG. 1(a) is lateral view of the arrangement of a polarizing platewhen in-plane luminance of the polarizing plate is measured, and FIG.1(b) is a plan view of the same.

[0060]FIG. 2(a) is a lateral view of the arrangement of a polarizingplate when in-plane optical retardation is measured, and FIG. 2(b) is aplan view of the same.

DESCRIPTION OF THE REFERENCE NUMERALS

[0061]1 glass substrate

[0062]2 binder

[0063]3 protective film

[0064]4 polarizing plate

BEST MODE FOR CARRYING OUT THE INVENTION

[0065] In the following, typical examples of the present invention aredescribed along with comparative examples. The method of measuring andthe method of evaluating physical properties employed in the presentinvention are as follows

[0066] Water vapor permeability was measured at 40° C. and 90%RH usingthe Mocon test (Permatran-W600 water permeability measurement deviceavailable from Mocon, Inc.).

[0067] The method for measuring wetting tension was in compliance withJIS-K6768.

[0068] The amount of change in optical in-plane retardation was measuredusing the following method. Specifically, as shown in FIG. 2(a), aprotective film 3 cut to a size length×width=100 mm×100 mm is adhered toa glass substrate 1 with a binder 2 made of acrylester-based base resinand an isocyanate-based curing agent interposed. Using a birefringenceanalyzer (Kobra automated birefringence analyzer available from OjiKeisoku, Inc.), optical in-plane retardation was then measured in eachof nine sections divided as shown in FIG. 2(b), and the average value R₀was obtained. After then subjecting this to an 80° C. atmosphere for 24hours, the optical in-plane retardation was measured in the same ninesections, and the average value R was obtained.

[0069] The surface shrinkage percentage was measured using the followingmethod. Specifically, a single protective film was cut to a sizelength×width=100 mm×100 mm, and after subjecting the film to an 80° C.atmosphere for 100 hours, the surface shrinkage percentage wasdetermined from Equation (1) below, where M is the length (mm) and T isthe width (mm).

Surface Shrinkage Percentage(%)={(100×100)−(M×T)}÷(100×100)×100  (1)

[0070] The polarization efficiency of polarizing plates was determinedusing the following method. Specifically, two polarizing plates werearranged on top of one another so that the polarization axes wereoriented in the same direction, and T₁ was taken to be the average valuefor light transmissivity measured continuously from a wavelength of 400nm to a 700 nm using a spectrophotometer. Two polarizing plates werethen arranged so that the polarization axes were perpendicular to oneanother, and T₂ was taken to be the average value for lighttransmissivity measured in the same manner. Polarization efficiency wasthus determined from Equation (2) below. A higher numerical valueindicates better polarization performance. $\begin{matrix}{{{polarization}\quad {efficiency}\quad (\%)} = {\sqrt{\frac{T_{1} - T_{2}}{T_{1} + T_{2}}} \times 100}} & (2)\end{matrix}$

[0071] The single transmissivity of a polarizing plate is the averagevalue for the light transmissivity of one polarizing plate measuredcontinuously from a wavelength of 400 nm to a 700 nm using aspectrophotometer. A higher numerical value indicates bettertransparency of the polarizing plate.

[0072] The humidity/heat resistance test of the polarization efficiencyof polarizing plates was carried out using the method below.Specifically, a polarizing plate was subjected to an atmosphere of 80°C. and 90%RH for 48 hours. The retention of the polarization efficiencyis a value obtained by dividing the polarization efficiency after thetest by the polarization efficiency before the test. A higher numericalvalue indicates better humidity/heat resistance.

[0073] Measurement and evaluation of hue shift were carried out usingthe following method. Specifically, using SZ-Σ80II available from NipponElectric Industries Co., Ltd., a value “a” and a value “b” for a singlepolarizing plate were measured before and after subjecting thepolarizing plate to an atmosphere of 80° C. and 90%RH for 24 hoursaccording to the Hunter-Lab method. A greater amount of change in avalue “a” or a greater amount of change in a value “b” indicates agreater hue shift.

[0074] Light leakage was evaluated using the in-plane luminance of apolarizing plate. Measurement and evaluation of the in-plane luminanceof a polarizing plate are carried out as follows. Specifically, twopolarizing plates 4 of dimensions 100 mm×100 mm cut from a longpolarizing plate at an angle of 4520 with respect to the polarizationaxis were adhered to either side of a glass substrate 1 with a binder 2interposed so that the polarization axes were perpendicular to oneanother, and this structure was subject to an atmosphere of 80° C. and90%RH for 24 hours, and then this structure was arranged on a backlight(Fuji Color Light Box 5000 available from Fuji Color Trading Co., Ltd.).The light source from the backlight was set to 100% reference value, andluminance was measured in each of nine sections divided as shown in FIG.1(b) using a luminance meter (LS-100 available from Minolta Co., Ltd.).Using the resulting values, the amount of light leakage as shown byEquation (3) below was determined. In this case, a closer numericalvalue to 1 indicates less light leakage.

[0075] In addition, light leakage was visually evaluated.

Amount of Light Leakage=(Average Luminance of {circle over (2)}{circleover (4)}{circle over (6)}{circle over (8)})÷(Average Luminance of{circle over (1)}{circle over (3)}{circle over (5)}{circle over(7)}{circle over (9)})  (3)

EXAMPLE 1

[0076] After dissolving 25 parts by weight of cyclic-olefin-based resin(Zeonor 1600R available from Zeon Corporation) in 75 parts by weight ofa mixed solvent of xylene, cyclohexane, and toluene (1:1:1 mixing ratioby weight), a film was fabricated by solution casting. Both sides of theresulting film were then subjected to a corona discharge treatment at atreatment intensity of 100 W/m²/min air, and a mixed solution ofpolyester polyol (Seikadyne LB available from Dainichiseika Color andChemicals Mfg. Co., Ltd.) and polyisocyanate (Seikadyne 3500A availablefrom Dainichiseika Color and Chemicals Mfg. Co., Ltd.) (1:11 mixingratio by weight) was coated, as a first anchor coat layer, on onesurface of the film so that the thickness after drying was 0.2 μm andallowed to dry. In addition, on the first anchor coat layer, a 5%aqueous solution of polyvinyl alcohol with an average degree ofpolymerization of 1500 and a degree of saponification of 99% was coatedas a second anchor coat layer so that the thickness after drying was 2μm and allowed to dry. Thus, a protective film having thereon two layersof anchor coat agents and having a thickness of 52 μm, a width of 550mm, and a length of 200 m was obtained. (Note that, immediately beforewinding the film, hot air at a temperature of 120° C. was introduced tothe film for 10 seconds while the film was under a draw ratio of −0.2%between rollers, and distortions of molecular chains in thecyclic-olefin-based resin were thereby corrected and the residualshrinking percentage was reduced.)

[0077] The water vapor permeability of the protective film obtained insuch a manner was 3.0 g/m²/24 hours, and wetting tension was 600 μN/cm(23° C.). The residual amount of solvent, the surface shrinkagepercentage, and the optical in-plane retardation R₀, R, and R−R₀ are asshown in Table 1.

EXAMPLE 2

[0078] A PVA film (Kuraray vinylon film VF-9X75R available from KurarayCo., Ltd., thickness 75 μm) was immersed for 5 minutes in an aqueoussolution that is 5000 parts by weight of water, 35 parts by weight ofiodine, and 525 parts by weight of potassium iodide such that the iodinewas adsorbed. After then uniaxially stetching the film in thelongitudinal direction to about 4.4 times in a 4% by weight of aqueoussolution of boric acid having a temperature of 45° C., the film wasdried while under tension to obtain a polarizing film.

[0079] Next, using a 5% aqueous solution of PVA having an average degreeof polymerization of 1800 and a degree of saponification of 99% as anadhesive, in such a manner that the thickness of the laminate structurethat results after drying is 1 μm, the adhesive in a non-dried state,

[0080] Next, in such a manner that the thickness of the laminatestructure that results after drying is 1 μm, the following process wascarried out. The polarizing film thus obtained and the pair ofprotective films obtained in Example 1 were arranged on top of oneanother with a 5% aqueous solution of PVA interposed therebetweenserving as an adhesive and with the anchor coat sides of the protectivefilms facing either side of the polarizing film. The aqueous solution ofPVA had an average degree of polymerization of 1800 and a degree ofsaponification of 99%. The structure was then secured between a rubberroller and a metal roller (the rubber roller has a diameter of 200 mmand the metal roller has a diameter of 350 mm, line pressure is 10kg/cm) and wound. The structure was left in the wound state (length of100 m) for 24 hours in a chamber having a temperature of 40° C. Theresults of the evaluation of the resulting polarizing plate are shown inTable 2.

EXAMPLE 3

[0081] A polarizing plate was obtained in the same manner as Example 2,using the protective film of Example 1 in a wound state which was storedat room temperature for a month. The results of the evaluation of thispolarizing plate are shown in Table 2.

Comparative Example 1

[0082] A polarizing plate was obtained in the same manner as Example 3,except that the second anchor coat layer made of polyvinyl alcohol wasnot provided. The results of the evaluation of this polarizing plate areshown in Table 2.

Comparative Example 2

[0083] A polarizing plate was obtained in the same manner as Example 1and Example 2, except that a corona discharge treatment was not carriedout, that both the first and second anchor coat layers were notprovided, and that an emulsion-type, 2-part epoxy acrylic-based adhesive(the base resin is E-Tec Emulsion AE943 available from Japan SyntheticRubber Co., Ltd. and the hardening agent is Aquanate 100 available fromNippon Polyurethane Industry Co., Ltd., (10:1 mixing ratio by weight))was used for the adhesive. The results of the evaluation of thispolarizing plate are shown in Table 3.

Comparative Examples 3 and 4

[0084] Two types of protective films having differing amounts of changein optical in-plane retardation were fabricated using the same castingsolution as that employed in Example 1. The residual amount of solvent,the surface shrinkage percentage, and optical in-plane retardation R₀,R, and R−R₀ of these films are as shown in Table 1. Using theseprotective films, polarizing plates were then obtained in the samemanner as Example 2.

[0085] The results of the evaluation of the polarizing plates are shownin Table 3. TABLE 1 Comparative Comparative Units Example 1 Example 3Example 4 Residual amount of ppm 1,000 8000 50 solvent Surface shrinkage% 0.12 1.05 1.50 percentage In-plane R₀ nm 0.2 0.9 3.3 retardation R nm3.7 10.2 14.7 R − R₀ nm 3.5 9.3 11.4

[0086] TABLE 2 Comparative Units Example 2 Exaample 3 Example 1 SingleTransmissivity % 41.9 41.9 41.9 Polarization efficiency % 99.9 99.9 99.9Retention of — 1.00 1.00 1.00 polarization efficiency Hue b Initialvalue — 2.28 2.29 2.33 After wet — 2.80 2.79 3.96 heating Hue a Initialvalue — −0.71 −0.71 −0.73 After wet — −0.88 −0.87 −1.18 heating Amountof light — 1.34 1.29 2.38 leakage Visual Evaluation of — None None SmallLight Leakage Amount

[0087] TABLE 3 Comparative Comparative Comparative Units Example 2Example 3 Example 4 Single Transmissivity % 41.9 41.9 41.9 Polarizationefficiency % 99.9 99.9 99.9 Retention of — 1.00 1.00 1.00 polarizationefficiency Hue b Initial value — 2.18 2.26 2.32 After wet — 4.36 2.912.88 heating Hue a Initial value — −0.76 −0.71 −0.68 After wet — −0.06−0.97 −0.99 heating Amount of Light — 2.60 6.91 7.40 leakage VisualEvaluation of — Small Yes Yes Light Leakage Amount

Industrial Application

[0088] The present invention makes it possible to provide a polarizingplate having high durability and high polarization efficiency with whichthe three factors that contribute to a degradation in liquid crystaldisplay performance under a high humidity/high temperature environment,drop in polarization efficiency, hue shift, and light leakage,substantially do not occur. In addition, the present invention makes itpossible to provide a polarizing plate, with which high adhesivestrength can be maintained between the protective film and thepolarizing film even after being stored for an extended period of time,and adhesion is completed in a short time.

What is claimed is:
 1. A polarizing plate comprising apolyvinyl-alcohol-based polarizing film, a protective film mainlycomposed of a cyclic-olefin-based resin, having thereon two anchor coatagent layers, and laminated on at least one side of the polarizing filmwith an adhesive: wherein the amount of change in optical in-planeretardation of the protective film is 5 nm or less after 24 hours in anatmosphere of 80° C., and the wetting tension of the surface to beanchor-coated of the protective film is 500 μN/cm (23° C.) or more;wherein the anchor coat agent layers include a first layer made ofpolyisocyanate and polyester polyol and/or polyether polyol, and asecond layer made of polyvinyl alcohol; and wherein the adhesive is madeof polyvinyl alcohol.